textproduct: Albany

WHAT HAS CHANGED

A few showers /isolated to widely scattered/ have continued over the west-central Mohawk Valley and western Capital District. No lightning noted by the isolated shower threat and PoPs were continued the next few hours before diminishing due to loss of the diurnal heating. Some patchy fog was also added overnight east of the southern Greens in Windham County near the CT River Valley. 15

Previous.. Models have come into decent agreement that the heaviest rainfall totals on Sunday night into Monday will be focused across far northwestern areas (western Adirondacks) and southern/southeastern areas (Catskills, mid Hudson Valley and western New England), with maximum amounts around two inches possible. Areas that saw heavy rainfall earlier in the week area most at risk for additional flooding concerns.

KEY MESSAGES

1) A slow moving cold front will result in periods of showers and thunderstorms across the entire region for Sunday night into Monday. With bursts of heavy rainfall expected, there will be the potential for isolated to scattered flash flooding, with areas that saw high rainfall amounts earlier in the week most susceptible to renewed flooding.

DISCUSSION

KEY MESSAGE 1...

A cold front and associated upper level trough will be very slowly moving eastward from the Great Lakes and into the Northeast for Sunday into Monday. Ahead of this boundary, it will be very moist across the region, with surface dewpoints well into the 60s, with some low 70s in valley areas. PWAT values will be exceeding two inches in many areas by early Monday and these values are 2-3 STD above normal. Guidance suggests rounds of showers and embedded thunderstorms will start impacting northwestern areas by later Sunday, with the highest coverage across the area for Sunday night through Monday afternoon.

Model soundings shows a low of ingredients that would favor the potential for heavy downpours and possible flash flooding. In addition to the high PWATs, there will be a moist profile throughout the entire troposphere, high freezing levels and a narrow skinny CAPE profile. This would result in highly efficient rainfall processes, allowing for heavy downpours.

There has been some question about where the heaviest rainfall will set up and some of the guidance has helped put this into better focus. Based on the latest info, northwestern areas (western Adirondacks) may see some of the heaviest downpours initially for late Sunday into Sunday night. For Monday, it appears far southern and southeastern areas may be most at risk, with the heaviest totals perhaps just south of the area into the northern mid Atlantic States. While the NBM suggests that there is a decent chance for a widespread 1" of rainfall (over 50 percent for many areas), it is not showing too high potential for over 2" (with under 20% for most of the region). Still, hi- res guidance, including the 12z SPC HREF, does suggest the potential for locally 2-3" in some areas that see repeated bursts of heavy rainfall for western and southern areas. The areas most at risk will be locations that saw heavy rainfall earlier in the week, as soils remain saturated and FFG is rather low for these areas. While far southern areas (such as near Poughkeepsie) are still in a rainfall deficit, locations not far away across northern parts of the mid Hudson Vally are fairly wet, so will need to closely monitor radar trends Sunday into Monday once showers and thunderstorms develop. There is currently a marginal risk for flash flooding for Sunday night into Monday for most of the area. Far southern areas (Dutchess and Litchfield Counties) also reach into the Slight Risk, which suggests the potential for isolated to scattered flash flooding.

Showers and thunderstorms will be winding down by Monday evening, as the best forcing and moisture shifts eastward, which will end the potential for any additional flooding by that time.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

Through 00Z/MON...VFR conditions begin the TAF period for KGFL/KALB/KPOU/KPSF with FEW-SCT cumulus, SCT-BKN mid level clouds and BKN high level clouds. Mid and high clouds will prevail tonight with the upper level trough and cold front approaching. With increasing low level moisture and the south/southwest boundary layer flow some lower stratus may develop at all the TAF sites. We have used TEMPO groups to bring in the lower stratus in the 08Z-12Z/Sun time frame with KALB/KGFL potentially having a lower MVFR deck at 1-1.5 kft AGL with some patchy mist. KPOU/KPSF may reach IFR levels at 800 ft AGL and KPSF may linger past 12Z/Sun. There may also be brief reductions to visibility to IFR/MVFR levels at KPSF. The lower stratus should burn off by 12Z-14Z/Sun at KGFL/KALB/KPOU with a few showers near KGFL. KPSF gradually improves to MVFR/VFR cigs towards 16Z/Sun. Mid and high clouds will linger through the afternoon with a pre-frontal disturbance approaching late. We used some PROB30 groups for KALB-KPSF late in the TAF cycle for a shower (less confident for a thunderstorm) and placed a PROB30 for thunderstorms at KGFL with MVFR conditions 17Z-23Z/Sun.

The south/southeast winds around 5 KT will become light to calm tonight at all the TAF sites except KALB will have a light breeze at 4-8 KT. The winds increase from the southeast to south at 8-15 KT in the late morning into the afternoon with some gusts 20-25 KT at KALB/KPSF.

Outlook...

Sunday Night: High Operational Impact. Definite SHRA...TSRA. Monday: High Operational Impact. Likely SHRA...TSRA. Monday Night: Low Operational Impact. Slight Chance of SHRA. Tuesday: Low Operational Impact. Slight Chance of SHRA. Tuesday Night: Low Operational Impact. Slight Chance of SHRA. Wednesday: Moderate Operational Impact. Chance of SHRA...TSRA. Wednesday Night: Moderate Operational Impact. Likely SHRA...TSRA. Thursday: High Operational Impact. Likely SHRA...TSRA.

ALY WATCHES/WARNINGS/ADVISORIES

CT...None. NY...None. MA...None. VT...None.